As part of the fabrication process for semiconductor devices such as integrated circuits (ICs), devices residing on a wafer typically undergo a heat treating or thermal annealing process, which may follow formation of one or more gate structures and implantation or doping of the wafer, for example. Annealing may serve several purposes, including physical repair of the silicon lattice structure following doping, and activation of the dopant.
Laser annealing is one particular annealing process that may be utilized in the fabrication of semiconductor devices, and may provide rapid annealing of selected portions of a semiconductor device. Laser annealing may be performed using many different techniques, including pulsed and stepped laser annealing. Laser annealing provides heating of selected portions of a silicon wafer, rather than heating of the entire wafer to a uniform temperature as in alternative annealing methods.
Present state of the art annealing methods such as laser annealing may result in uneven heating or temperature non-uniformity of surfaces of a semiconductor device, due at least in part to varying topographies or topologies of a device that are created during the fabrication process, and the nature of laser light being somewhat pattern dependent. For example, the topography of a semiconductor device may vary across the surface of the device. A surface on top of a substrate, in an area between two gates, may be in a lower relative vertical position than a top surface of a gate, for example. Because the topography differs among these surface points, a laser used in an annealing process may be absorbed or reflected differently depending on the pattern of the surface being irradiated. This may result in uneven heating among these surface points, which may result, for example, in the production of undesirable physical characteristics in a semiconductor device. A need exists, therefore, of a method and apparatus of reducing these thermal effects.